In the history of strategic military operations,
it has long been public knowledge that Allied operations in the
Pacific during World War II were indebted to the breaking of the
Japanese operational communications codes. More recently it has
been revealed that the British were able to break the strategic
communications code by which Hitler received information and issued
directives to his senior commanders. High command levels should
have and did get top priority in American attempts to safeguard
communications against similar breaches. With the men at the
tactical level not really wanting signal security gear, there was a
relatively modest attempt in the U.S. Army to develop new equipment
for that level until the need became more evident.

Signal security equals a combination of people, equipment, and systems. People participating in tactical operations have a natural dislike for signal security measures; they prefer to
conduct business in the simplest, most direct manner possible. Early in Vietnam, possible in most cases meant whatever superiors
would permit in the tactical situation involved. The people part of
the equation did not improve until the chain of command became convinced of the need for strict communications discipline. The conviction grew in proportion to information about the threat, and interest and participation grew as equipment and systems improved. The signal security problem was never fully resolved during the Vietnam era despite many improvements and much hard work. It was, and still is, one of the most difficult problems facing tactical communicators.

Along with the need to communicate as rapidly
and directly as possible during combat, another factor worked
against effective communications security: a soldier in the thick
of battle feels the need for friendly assurance. This assurance can
come from talking-to anyone else who has a radio. When this
happens, chances are that little thought is given to what
information is actually being transmitted.

Before secure voice equipment was in general
use, oral communications requiring any secrecy had to be
painstakingly coded

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and decoded manually. All too often coding was
circumvented in favor of simplicity, speed, and assurance. The
tactical communicator needed some type of voice encryption device.

In 1965, when he was the U.S. Army, Vietnam,
signal officer, Colonel Kenneth Ring recalled that there were some
eight hundred KY-8 security devices in a stateside depot. These
devices had no mounting brackets or connecting cables because their
application had not been settled. Colonel Ring requested, on behalf
of U.S. Army, Vietnam, that a new equipment training team be sent
to Vietnam to demonstrate the devices and discuss their tactical
uses; the team arrived in August 1965. From this start, the
security device applications and improvements progressed through
some tortuous evolutions.

Voice security devices were issued to the field
units in Vietnam beginning in 1965 with the KY-8 for stationary or
vehicular use; the KY-8 was fully distributed by the third quarter
of fiscal year 1968. The KY-28 was issued for use in aircraft
beginning in 1967 and ending a year later. The KY-38, for manpack
or mobile use, also was issued initially in 1967 and was fully
distributed in 1968.

The voice security gear, like most newly
developed equipment, had its problems. The main cause of failure
was heat. The KY-8 had to be kept in well ventilated surroundings
and away from direct sunlight. During a 1969 presidential visit, an
overheated KY-8 temporarily stopped secure voice communications
between II Field Force headquarters and Tan Son Nhut.

The 199th Light Infantry Brigade station at Xuan
Loc, in the 11 Field Force commanding general's secure FM voice
net, continually broke down. Many pieces of equipment were
generating heat in a poorly ventilated bunker and causing the KY-8
to fail. When it was moved to a cooler location, the KY-8 operated
normally. Commanders and communicators became aware that, for
reliable communications, the security equipment had to operate in
the coolest possible environment.

In at least one case the ingenuity of a well
intentioned communicator backfired. First, he placed a filled
Lyster (water) bag over the KY-8 to cool it, but the device still
overheated. Next, he removed the cover of the KY-8 to increase
ventilation. That improved the operation of the KY-8 but violated
security by exposing the equipment to view and giving the enemy an
opportunity to intercept intelligible signals.

In a successful innovation, the 125th Signal
Battalion engineered and installed a secure land line to expedite
spot reports be-

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tween the 372d Radio Relay Company and the 25th
Infantry Division G-2. The battalion, operating two KY-8's in
essentially a back-to-back test mode, replaced the short
back-to-back cable with spiral-four cable of the required length.
This system worked with almost no trouble and with very high
quality.

During September 1968, the PRC-77 and KY-38
combination was issued down to the infantry battalion level,
providing for the first time secure voice communications to
infantry companies and in the battalion command nets. At the
company level plans and operations could be discussed rapidly,
safely, and explicitly without fear of enemy detection. Field units
used two methods to offset the weight disadvantage (over 50 pounds)
of the PRC-77/KY-38 package. One was to use the equipment fully by
having one man carry the PRC-77 radio and another the KY-38. The
second was to move the field unit as normal, then have supporting
aircraft fly in the equipment for use in static or night defensive
positions.

In the fall of 1969, reports on NESTOR (code
name given narrowband secure voice equipment) utilization were
revealing. Many units under the operational control of the II Field
Force were not using their KY-38's as much as desired. The
PRC-77/KY-38 when carried by one man, as intended, was just too
heavy. Other units reported that they needed VRC-12/KY-38
interconnecting cables. They wanted to use the smaller KY-38 in
lieu of the KY-8. The KY8 was prone to overheat and ran on
generated power. Power was limited at fire support bases, and the
field troops thought it unwise to run the noisy generators at
night. The KY-38, on the other hand, was battery powered. Acting on
this feedback, Electronics Command Laboratories went into an
emergency production of interconnecting cables for the VRC-12 and
the KY-38 and by late 1969 had produced three hundred. A
substitution of the KY-38 for the KY-8 in vehicles was also agreed
upon.

One of the most serious equipment problems in
the field was the lack of kits and special cables for installing
NESTOR gear in aircraft and vehicles. The installation kits and
most of the cables was a supply responsibility of the Electronics
Command. There was a variety of kits which adapted NESTOR equipment
to the tactical series radios used in vehicles and aircraft. The
initial supply of kits, once they had been developed, was adequate
early in fiscal year 1969. As the use and uses of the equipment
increased, however, kits and cable components became increasingly
hard to find. The so-called X-mode cable for the KY-8 was also in
short supply. Another aspect of the kit shortage came to light
during the U.S. withdrawal from Vietnam. Although retrieving the
NESTOR

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equipment from vehicles was no problem
redistributing it was often haphazard. A similar situation existed
with KY-28's in aircraft, principally helicopters. Losses and
evacuations of aircraft which had been fitted for the equipment
made the shortage worse, since most of the replacement aircraft did
not come with the kits installed.

The number of KY-28 keying devices for the
NESTOR family of equipment was adequate when units were operating
in one locale; when divisional units were dispersed (the normal
practice), more keying devices were needed. The 101st Airborne
Division recommended that keying devices for the KY-28 and KY-38 be supplied as required. In July 1969, II Field Force
established a common NESTOR key list for all units operating in the
III Corps zone. To maintain compatibility, key changes had to occur
simultaneously in all units. The time chosen for this change was
midnight, tactically the worst possible time because the greatest
number of enemy contacts occurred from 2200 to 0200. Moreover,
where several units shared the same keying device, having to move
at night to change key settings was inconvenient and dangerous and
added to the reasons for not using the equipment. Later the time of
the daily NESTOR key change was moved to 0600.

As the use of communications security equipment
increased in Vietnam, so did the need for logistical support. A
reorganization was approved by the commanding general of U.S. Army,
Vietnam, in mid-1967. The revised structure consisted of the
Communications Security Logistics Support Center, Vietnam, which
functioned as a general support facility serving U.S. Army,
Vietnam, with six subordinate units strategically located in the
four corps areas. The center was also assigned the mission of
organizing, training, and deploying seven contact detachments to
augment direct support to the combat divisions. Support began to
improve.

Security codes were another problem. The early
units had not been very conscious of communications security, and
the unauthorized practice of using homemade communications security
codes and shackles eventually became widespread. This dangerous
practice; which persisted throughout the conflict and which gave
users a false sense of security, was probably more dangerous than
communicating in the clear. As the number of units burgeoned and
the need for compartmenting code systems grew, U.S. Army, Vietnam,
requested and received from the National Security Agency a whole
series of preprinted codes to cover the expansion. These codes,
while not perfect, were a great improvement in both the employment
and distribution of such systems. Getting the infan-

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tryman under fire, or the helicopter pilot
supporting him, to employ the codes was another matter.

The continuing need for easier authentication
and more reliable means for passing limited classified traffic led
to a new development in the later stages of the conflict: the
KAL-55B authentication wheel, or "whiz wheel," a circular
authentication table in a plastic covered disc. This innovation
simplified communications security measures to a level acceptable
to most users.

Signal security, particularly in voice radio
transmissions, was a major problem area throughout the period of
combat operations in Vietnam. Army Regulation 380-40, Department
of the Army Policy for Safeguarding Communications Security
Information, assigns responsibility for this type of security
to both the commander and the individual. All users of
communications facilities were more or less aware of their
vulnerability to enemy intercept, analysis, and decoding, and of
the need for authentication and encoding. The gap between this
knowledge and actual practice was immense, and in Vietnam it seemed
at times an insurmountable problem.